Composite materials are used in the manufacture of a wide variety of structures and component parts due to their high strength and rigidity, low weight, corrosion resistance and other favorable properties. For example, in the aerospace industry, composite materials are becoming widely used to manufacture aerospace structures and component parts for aerospace structures such as aircraft ribs, spars, panels, fuselages, wings, wing boxes, fuel tanks, tail assemblies and other component parts of an aircraft because they are lightweight and strong, and therefore provide fuel economy and other benefits. As used herein, the term “composite structure” means a structure that is manufactured, fabricated or assembled, in whole or in part, from one or more component parts made from composite materials (i.e., composite components) including, without limitation, aerospace structures.
One type of composite material commonly used in the aerospace industry is carbon fiber reinforced plastic (“CFRP”). CFRP generally comprises one or more composite layers or plies laminated together to form a sheet, laminate or layup. Each of the composite layers or plies comprises a reinforcement material and a matrix material. The matrix material surrounds, binds and supports the reinforcement material, and is generally a non-conductive polymer such as an epoxy resin. For aerospace applications, an aerospace grade resin is used as the matrix material, typically having four (4) epoxide groups in each epoxy monomer molecule to form multiple connections. The reinforcement material provides structural strength to the matrix material and the CFRP, and generally consists of strands of carbon fiber or carbon filaments, which are electrically conductive. Carbon fibers are typically formed as carbon tows comprising a defined number of carbon filaments. For aerospace applications, carbon tows may comprise bundles of carbon filaments ranging from about 1,000 to about 24,000 carbon filaments; carbon tows having up to about 300,000 carbon filaments may be used in other applications.
It is desirable to increase the amount of carbon in CFRP to further improve mechanical and/or electrical properties of composite structures without increasing weight or disturbing other desirable properties. But, simply increasing the amount of carbon fiber reinforcement material in CFRP does not meet this goal and is not cost efficient. Other forms of carbon, such as graphene, which has exceptional mechanical strength and thermal conductivity, would have beneficial effects in composite structures. Graphene is a hexagonal array of carbon atoms extending over two dimensions (i.e., it is one atom thick) that is typically produced in small flakes (or nanoplatelets). Each carbon atom in graphene is covalently bonded to three other carbon atoms, providing exceptional strength. However, mixing graphene into an epoxy resin comprising carbon fibers makes the epoxy resin weaker to strain in every direction because graphene will not bond with the carbon fibers and does not interact much with the epoxy resin.
Accordingly, there is room for improving the mechanical and electrical properties of composite structures and related methods for manufacturing composite structures that provide advantages over known composite structures and manufacturing methods.